Holle Finch leaves her home that was recently redesigned as a passive solar house by architect Thomas Doerr of Boulder. The house is located in Denver and has won numerous awards. Overhangs, southward-facing windows and thermal storage walls help the house save on energy without the use of solar panels.

The renovated Finch home is full of interior light from its southern and eastern exposure — enough light for Bruce the dog to bask in.

A cross section of the Finch home shows the angles of the winter and summer sun and how overhangs tame the fierce summer sun while maximizing solar heat in winter.

The house is cool, but most homes are these days, in the sweltering summer heat. Here, though, it should be hot.

Or at least, the air-conditioning should be blasting.

But in Holle Finch’s red and white house on Sherman Street in Denver, there is no air conditioning. Instead, her home makes use of passive solar energy to stay cool. Overhangs block the high summer rays of the sun; this winter, windows on the southern wall will allow the lower-angled rays to heat the living space directly. Inside, brick catches the cool of the night air, releasing it throughout the day.

Passive solar energy methods include low-tech solutions such as these. They’re used to heat, cool, light and ventilate a building, as distinguished from better-known mechanical devices, such as solar panels — active solar.

“I think of it like a cake,” he said. “Active solar is like the icing. But you need a good cake to put that icing on.”

There are three key passive solar systems, Doerr says. Direct gain uses the sun to heat the house in winter. A passive solar house is designed with plenty of southern glass, but in a way that also blocks the summer sun.

There are thermal storage walls, which include materials like stone or brick to absorb colder night air and then release it during the day.

Finally, the use of a sunspace works like a small greenhouse, pulling heat in and acting like a furnace.

Doerr is quick to point out that it doesn’t cost anything to orient a building correctly. He says homeowners can save 80 to 90 percent of their energy budget by using passive solar techniques.

Finch says she’s noticed how friends with similar-sized houses spend nearly double what she does on her energy bill. While her house is small, it’s effective. Two curved roofs extend into overhangs for her windows. Tin siding, exposed wood and clean stucco radiate a modern, slightly industrial feel.

“Passive solar was not part of my vocabulary before,” Finch said. “You hear about using cork floors or bamboo aesthetics but not fixing the structure itself. It’s all important. The design has a purpose, a bigger, lasting impact.”

The three strategies are not exclusive. Doerr says early passive solar houses in the 1960s and ’70s cooked during the day from the southern glass but were freezing at night because it let out all of the heat. Now, by adding such thermal mass as brick, stone or concrete, designs help keep the temperature balanced.

“Buildings use almost half of the energy (people) use,” Doerr said. “Eliminate that, and it’s a huge step toward treading lighter on the planet. Driving a Prius isn’t going to save the world.”

Doerr has designed many passive solar homes in Colorado and features many as examples in his book. The Moore house in Evergreen is a net-zero energy home, entirely off the grid, meaning it produces more energy than it uses — with the help of active solar.

For homeowners looking to use passive solar without starting over or performing extensive remodeling, a sunspace is the most effective option. The Bien house in Denver is more than 100 years old. Not wanting to ruin the original look by changing the walls for energy efficiency, Doerr simply added a sunspace. Now the Biens aren’t paying for any of the energy lost through the old walls. The sun makes for free heat.

Originally, Finch was just looking to make her home more eco-friendly with the remodel. Building a passive solar home was only a little more expensive at the start, but she said it was well worth it.

“It’s just my house now,” she said. “It’s just where I live. It functions on its own with no worries.”

Doerr’s book tells people what they need to know to outfit their house for passive solar, including the angles for overhangs and the percentage of southern glass needed. While many people know about active systems, he said, there isn’t a trend toward passive techniques.

“The public doesn’t know enough to demand it,” he said. “I’m in a niche market, and I want to change that.”

As the sun sets for the day, Finch will open her house, letting the night air sweep in and collect for tomorrow. With more sun than Miami and cooler nights, Doerr says this is the optimal place for passive solar.

“Colorado is ideal,” he said. “Here it’s easy. It’s perfect. Other areas can do it, but you don’t get better than the West.”

Dear Amy: My grandfather is well-off. He saved and spent very little throughout his life. For many years, he has promised my mother and me that we would receive a sizable inheritance. My grandmother died several years ago, and we are the only close family members he has left.